Etching method, etching apparatus and storage medium

ABSTRACT

A method for etching a silicon oxide film on a target substrate where an etching area is partitioned by pattern layers and stopping the etching before a base layer of the silicon oxide layer is etched is disclosed. The method includes heating the target substrate in a vacuum atmosphere and intermittently supplying, as an etching gas, at least one of a processing gas containing a hydrogen fluoride gas and an ammonia gas in a pre-mixed state and a processing gas containing a compound of nitrogen, hydrogen and fluorine to the target substrate from a gas supply unit multiple times.

CROSSREFERENCE

This application claims priority to and benefit of Japanese PatentApplication No. 2014-136114, filed on Jul. 1, 2014, the entire contentof which is herein incorporated by reference for all purposes.

FIELD OF THE INVENTION

The disclosure relates to a technique for performing an etching processby supplying a processing gas to a surface of a target substrate.

BACKGROUND OF THE INVENTION

As types of semiconductor devices are increased, it is required to dealwith various new processes in a semiconductor manufacturing field. Forexample, there is a process of etching a SiO₂ (silicon oxide) layerwhere silicon walls as pattern layers are arranged in parallel at aregular interval and an etching area is partitioned by the silicon wallsand then stopping the etching in the middle of the SiO₂ layer.

As for a method for etching a SiO₂ layer, there is known a methoddisclosed in, e.g., Japanese Patent Application Publication No.2009-158774, which performs a chemical oxide removal process using HF(hydrogen fluoride) gas and NH₃ (ammonia) gas. In this method, HF gasand NH₃ gas are supplied to a processing chamber while heating asemiconductor wafer (hereinafter, referred to as “wafer”) in order toetch the SiO₂ layer formed on a surface of the wafer. The gases reactwith SiO₂, thereby generating (NH₄)₂SiF₆ (ammonium silicofluoride). SiO₂is removed by sublimating (NH₄)₂SiF₆ by heating.

In the case of performing the process of stopping the etching of theSiO₂ layer in the middle of the SiO₂ layer, it is required to ensuregood roughness of the surface of the SiO₂ layer after the etching. Inthe case of etching the SiO₂ layer along the pattern layers as in theabove example, it is required to suppress microloading in which anetching speed varies depending on a density of the pattern.

SUMMARY OF THE INVENTION

In view of the above, the disclosure provides a technique capable ofimproving roughness and suppressing microloading in etching a SiO₂ layerwhere an etching area is partitioned by pattern layers and stopping theetching before a base layer is etched.

A method for etching a silicon oxide film on a target substrate where anetching area is partitioned by a pattern layer and stopping the etchingbefore a base layer of the silicon oxide film is etched comprisesheating the target substrate in a vacuum atmosphere and intermittentlysupplying, as an etching gas, at least one of a first processing gascontaining a hydrogen fluoride gas and an ammonia gas in a pre-mixedstate and a second processing gas containing a compound of nitrogen,hydrogen and fluorine to the target substrate from a gas supply unit inmultiple cycles.

A substrate processing apparatus comprises a processing chamber having amounting part configured to mount thereon the target substrate, a gassupply unit, having a plurality of gas supply holes facing the targetsubstrate, configured to supply, as an etching gas, at least one of aprocessing gas containing a hydrogen fluoride gas and an ammonia gas ina pre-mixed state and a processing gas containing a compound ofnitrogen, hydrogen and fluorine to the target substrate mounted on themounting part, a vacuum exhaust unit configured to evacuate theprocessing chamber, and a control unit configured to output a controlsignal that controls the gas supply unit to intermittently supply theetching gas to the target substrate from the gas supply unit in multiplecycles.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the disclosure will become apparent from thefollowing description of embodiments, given in conjunction with theaccompanying drawings, in which:

FIG. 1 is a vertical cross sectional view showing an etching apparatusaccording to an embodiment;

FIG. 2 is a vertical cross sectional view showing a vicinity of asurface of a wafer;

FIG. 3 is a vertical cross sectional view showing a vicinity of asurface of a wafer after an etching process;

FIG. 4 explains gas supply transition in an embodiment;

FIGS. 5 to 7 explain an operation of an embodiment;

FIGS. 8 to 10 explain etching states on the wafer surface;

FIG. 11 explains gas supply transition in another embodiment;

FIG. 12 is a vertical cross sectional view showing a vicinity of a wafersurface in another embodiment;

FIG. 13 is a cross sectional view of a wafer after an etching process ina test example and a comparative example;

FIG. 14 is a cross sectional view of the wafer after the etching processin the test example;

FIG. 15 is a cross sectional view of the wafer after the etching processin the comparative example;

FIG. 16 is a perspective view showing a wafer surface state in the testexample; and

FIG. 17 is a perspective view showing a wafer surface state in thecomparative example.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an etching apparatus according to an embodiment will bedescribed. As shown in FIG. 1, an etching apparatus includes aprocessing chamber 1 configured as a vacuum chamber having anapproximately cylindrical shape as a horizontal cross sectional shape.Provided at a side wall of the processing chamber 1 is aloading/unloading port 12 through which a target substrate, e.g., awafer W having a diameter of 300 mm, is transferred. A gate valve 13 foropening/closing the loading/unloading port 12 is provided at theloading/unloading port 12.

A cylindrical stage 2 for mounting thereon a wafer W is provided in theprocessing chamber 1. Seven supporting pins 21 for supporting the waferW protrude from the top surface of the stage 2 with a gap of, e.g.,about 0.3 mm, from the surface of the stage 2 along a circumferentialdirection of the stage 2. Three through holes 22 spaced from each otherat a regular interval along the circumferential direction are formedthrough the stage 2 and a bottom wall of the processing chamber 1. Upthrust pins 24 for transferring a wafer W are provided in the throughholes 22 to protrude and retreat with respect to the upper surface ofthe stage 2 by an elevation unit 23. A lower part of each of theupthrust pins 24 is covered by a bellows 25 for sealing the processingchamber 1. A heater 26 serving as a heating unit is provided in thestage 2, so that the wafer W mounted on the stage 2 is heated to a settemperature.

A gas exhaust port 14 is provided at a bottom surface of the processingchamber 1. A gas exhaust line 15 is connected to the gas exhaust port 14and also connected to a vacuum pump 18 serving as a vacuum exhaustmechanism via a pressure control valve 16 and an opening/closing valve17. The pressure control valve 16 and the opening/closing valve 17 areinstalled in that order from the gas exhaust port 14 side. Thecomponents such as the gas exhaust line 15 and the like form a vacuumexhaust unit.

An opening 11 is formed at the top surface of the processing chamber 1.A gas supply unit 3 is provided to block the opening 11. A diffusionplate 30 is provided at the gas supply unit 3 to face a mounting surfaceof the stage 2. The diffusion plate 30 is formed in a circular plateshape and made of a material having a high thermal conductivity, such asaluminum or the like. Further, the diffusion plate 30 is configured as apunching plate having a plurality of gas supply holes 31, each having adiameter ranging from about 0.5 mm to 2.0 mm, penetrating therethroughin a thickness direction. The gas supply holes 31 are arranged in amatrix pattern. Formed above the diffusion plate 30 is a dispersionspace 32 for a processing gas supplied into the processing chamber 1.

The gas supply unit 3 has two gas supply lines 33 and 34 communicatingwith the dispersion space 32. A downstream end of an NH₃ gas supply line40 is connected to an upper end of the gas supply line 33. A downstreamend of an HF gas supply line 50 is connected to an upper end of the gassupply line 34. First, the NH₃ gas supply line 40 side (NH₃ gas supplysystem) will be described. An NH₃ gas supply source 41, a flow ratecontrol unit 42, and valves V3 and V1 are installed in the NH₃ gassupply line 40 in that order from an upstream side thereof. A downstreamend of an N₂ (nitrogen) gas supply line 43 for supplying a carrier gas(dilution gas) is connected between the valves V3 and V1 in the NH₃ gassupply line 40. An N₂ gas supply source 44, a flow rate controller 45and a valve V5 are installed in the N₂ gas supply line 43 in that orderfrom an upstream side thereof. An upstream end of a bypass line 46 isconnected between the NH₃ gas supply source 41 and the flow ratecontroller 42 in the NH₃ gas supply line 40. A downstream end of thebypass line 46 is connected to the gas exhaust line 15. A flow ratecontroller 47 and a valve V7 are installed in the bypass line 46 in thatorder from the upstream side thereof.

Next, the HF gas supply line 50 side (HF gas supply system) will bedescribed. An HF gas supply source 51, a flow rate controller 52, andvalves V4 and V2 are installed in the HF gas supply line 50 in thatorder from an upstream side thereof. A downstream end of an Ar gassupply line 53 for supplying a carrier gas (dilution gas) is connectedbetween the valves V4 and V2 in the HF gas supply line 50. An Ar gassupply source 54, a flow rate controller 55 and a valve V6 are installedin the Ar gas supply line 53 in that order from an upstream sidethereof. An upstream end of a bypass line 56 is connected between the HFgas supply source 51 and the flow rate controller 52 in the HF gassupply line 50. A downstream end of the bypass line 56 is connected tothe gas exhaust line 15. A flow rate controller 57 and a valve V8 areinstalled in the bypass line 56 in that order from the upstream sidethereof.

A heater 35 is provided to surround the gas supply lines 33 and 34, thedispersion space 32 and the diffusion plate 30. The dispersion space 32and the diffusion plate 30 are set to, e.g., about 140° C.±10° C. Thegas supply lines 33 and 34 are set to, e.g., about 75° C. Further, aheater (not shown) is provided in the processing chamber 1. An innersurface of the processing chamber 1 is set to, e.g., about 140° C.±10°C. Therefore, it is possible to control eduction of a by-product, e.g.,NH₄F, generated by reaction between NH₃ gas and HF gas in the gas supplylines 33 and 34 or the like. Accordingly, generation of particles issuppressed.

The etching apparatus include a control unit 9. The control unit 9 is,e.g., a computer, including a program, a memory, and a CPU. The programhas a group of steps for realizing a series of operations to bedescribed later, so that opening/closing of the valves V1 to V8, flowrates of gases, a pressure in the processing chamber 1 and the like arecontrolled by the program. The program is stored in a computer storagemedium, e.g., a flexible disk, a compact disk, a hard disk, amagneto-optical disk or the like, and installed in the control unit 9.

Hereinafter, an operation of an embodiment of the disclosure will bedescribed. First, there will be described an example of a surfacestructure of a wafer W as a target substrate to be loaded into theprocessing chamber 1. FIG. 2 shows a surface structure of the wafer W inthe middle of a semiconductor device manufacturing process. FIG. 3 showsa surface structure of the wafer W after an etching process. In thissurface structure, a plurality of walls 62 extending horizontally isformed in parallel by etching a Si (silicon) layer 60 and grooves 63 areformed between the walls 62. SiO₂ fills an area around the walls 62which includes the grooves 63. If the area filled with SiO₂ is referredto as a SiO₂ layer 61, the surface of the SiO₂ layer 61 is leveled withthe top surfaces of the Si walls 62. This surface structure may beexplained in another way. In other words, protrusion patternscorresponding to pattern layers formed of the Si walls 62 are embeddedin the SiO₂ layer 61 so that the surface of the SiO₂ layer 61 is locatedat the same vertical position as the top surfaces of the walls 62.

Since the SiO₂ layer 61 is a target to be etched by an etchingapparatus, the SiO₂ layer 61 has an etching area partitioned by theprotrusion patterns (walls) 62.

The etching process of the SiO₂ layer 61 formed at the wafer W will bedescribed with reference to FIG. 4 showing a time chart of supply (ON)and supply stop (OFF) of gases. The wafer W is mounted on the stage 2 bycooperation of an external transfer arm (not shown) and the upthrustpins 24 and heated to, e.g., about 115° C., by the heater 26. Forexample, the gas supply lines 33 and 34 are set to about 75° C. and aperipheral wall of the dispersion space 32 is set to about 130° C. bythe heater 35 installed at the gas supply unit 3.

The gate valve 13 is closed and the processing chamber 1 is airtightlysealed. Then, at a time t₀ shown in FIG. 4, the valves V1 and V5 areopened and N₂ gas is supplied at a flow rate of, e.g., about 500 sccm.Further, the valves V2 and V6 are opened and Ar gas is supplied at aflow rate of, e.g., about 500 sccm. N₂ gas and Ar gas are dispersed inthe dispersion space 32 and then supplied into the processing chamber 1through the gas supply holes 31 formed at the diffusion plate 30.

Next, a process of intermittently supplying HF gas and NH₃ gas to thewafer W is carried out. At a time t₁, NH₃ gas is ON. “ON” denotes supplyof NH₃ gas from the gas supply unit 3 into the processing chamber 1.Specifically, at a time earlier than the time t₁, the valve V3 is closedand the valve V7 is opened as shown in FIG. 5, so that NH₃ gas bypassesthe processing chamber 1 and flows toward the gas exhaust line 15through the bypass line 46. After the flow rate becomes stable, thevalve V3 is opened and the valve V7 is closed as shown in FIG. 6 at thetime t₁. Accordingly, NH₃ gas is diluted with N₂ gas and flows into thedispersion space 32 through the gas supply line 33. Then, this gas ismixed with Ar gas supplied through the gas supply line 34. Next, thisgas is injected to a processing atmosphere of the processing chamber 1through the gas supply holes 31 and supplied to the wafer W. In FIG. 5and the following drawings, closed valves are hatched for convenience ofillustration.

In the HF gas supply system, the valve V4 is closed and the valve V8 isopened as shown in FIG. 5 at a time earlier than the time t₁, so that HFgas bypasses the processing chamber 1 and flows toward the gas exhaustline 15 through the bypass line 56. After the flow rate becomes stable,the valve V4 is opened and the valve V8 is closed as shown in FIG. 7 ata time later than the time t₁ by ΔT, i.e., at a time t₂ later than thetime t₁ by, e.g., about 0.5 sec to 15 sec. Accordingly, HF gas isdiluted with Ar gas and flows toward the dispersion space 32 through thegas supply line 34. As a consequence, NH₃ gas diluted with N₂ gas and HFgas diluted with Ar gas reach the dispersion space 32. The two gases aresufficiently mixed in the dispersion space 32, because the conductanceis low due to a small diameter of the gas supply holes 31. The gaseousmixture is discharged to a processing atmosphere through the gas supplyholes 31 and supplied to the wafer W.

At a time t₃ after the supply of the gaseous mixture for a period oftime Ta, e.g., about 2 sec, the valves V3 and V4 are closed and thevalves V7 and V8 are opened. Accordingly, the supply of NH₃ gas and HFgas is switched from the processing chamber 1 side to the bypass lines46 and 56 side, and NH₃ gas and HF gas are OFF at the same time (thesupply of both gases into the processing chamber 1 is stopped at thesame time). Such a series of supply cycles are performed again afterabout 5 sec to 15 sec elapses from the time t₃. Then, the supply cyclesare repeated a preset number of times. In this example, the supply ofNH₃ gas into the processing chamber 1 is started at a time t₄ afterabout 5 sec to 15 sec elapses from the time t₃ and the supply of HF gasis started at a time later than the time t₄ by ΔT (after about 0.5 secto 15 sec elapses from the time t₄). Therefore, the gaseous mixture ofNH₃ gas and HF gas is supplied to the wafer W for the period of time Ta,e.g., about 2 sec. These supply cycles are performed multiple times atan interval of Tb, e.g., about 5 sec to 20 sec. NH₃ gas is suppliedearlier than HF gas by ΔT, e.g., about 0.5 sec to 15 sec. FIG. 4 is animage showing an example of a sequence for implementing the disclosure.

From the time t₀ to the completion of the supply cycles, a pressure inthe processing chamber 1 is set to, e.g., about 250 Pa (1.88 Torr). Flowrates of N₂ gas and Ar gas are set to about 500 sccm. A flow rate of NH₃gas is set to about 100 sccm. A flow rate of HF gas is set to about 200sccm. After the supply cycles are repeated a preset number of times, N₂gas and Ar gas are supplied into the processing chamber 1 and, then, thewafer W is unloaded from the processing chamber 1.

Hereinafter, there will be described the surface state of the wafer Wduring the above series of processes. FIGS. 8 to 10 are schematicdiagrams (images) showing the surface state of the wafer W during thegas supply sequence shown in FIG. 4. These schematic views are imagesfor intuitively recognizing the correspondence between the etching andthe gas supply sequence, not accurately illustrating the surface state.

FIG. 8 shows a state in which NH₃ gas is supplied to the wafer W beforeHF gas is supplied to the wafer W. In this state, NH₃ molecules 81 areadsorbed onto the surface of the SiO₂ layer 61 (Although the entiresurface of the SiO₂ layer 61 is actually covered with NH₃ molecules, itsschematic state is illustrated in FIG. 8).

When the processing atmosphere is switched to the gaseous mixture of HFgas and NH₃ gas, the SiO₂ layer 61 reacts with HF molecules 80 and NH₃molecules 81 as shown in FIG. 9, thereby generating a reactionby-product 82, e.g., (NH₄)₂SiF₆, water or the like. Next, the supply ofNH₃ gas and HF gas is stopped and only N₂ gas and Ar gas flow as purgegases. Therefore, unreacted HF molecules 80 and unreacted NH₃ molecules81 are removed by the purge gases. At this time, the reaction by-product82 such as (NH₄)₂SiF₆, water and the like is volatilized (sublimated) byvacuum evacuation and removed by the purge gases as shown in FIG. 10.Accordingly, the SiO₂ layer is gradually removed by the sublimation ofthe reaction by-product 82.

In the above embodiment, NH₃ gas is firstly supplied and, then, HF gasis supplied. Although the etching occurs only by supplying HF gas toSiO₂, the reaction speed is increased by supplying NH₃ gas as well as HFgas, because NH₃ gas reacts as a catalyst (NH₃ gas is referred to as acatalyst even though NH₃ itself reacts). By adsorbing NH₃ gas onto thewafer W and then supplying the gaseous mixture of HF gas and NH₃ gas, HFgas and NH₃ gas easily react with the SiO₂ layer 61. As a result, theetching process becomes stable and rapidly proceeds.

The SiO₂ layer 61 is etched by the gaseous mixture. The reactionby-product 82 thus generated serves as an etching protective film. Anexposed area of the SiO₂ layer 61 per unit area is smaller in a densepattern area than in a sparse pattern area. Therefore, a thickness ofthe protective film adhered to the SiO₂ layer 61 is large and this leadsto a decrease of the etching speed. Accordingly, in the case ofperforming an etching process by supplying HF gas and NH₃ gasconsecutively, the microloading in which an etching speed becomes slowerin the dense pattern area than in the sparse pattern area may occur. Inthe above-described embodiment, the supply of HF gas and NH₃ gas isstopped at an interval of 2 sec and the surface of the wafer W is purgedby N₂ gas and Ar gas. As a consequence, the protective film issublimated during the supply stop of HF gas and NH₃ gas. In other words,the surface state returns to an initial state. Therefore, the etchingspeed is not different between the dense pattern area and the sparsepattern area, and the microloading is avoided.

In the above-described embodiment, the supply of NH₃ gas and HF gas isstopped at the same time. Therefore, the reaction of the SiO₂ layer 61with NH₃ gas and HF gas is stopped at the same time on the entiresurface of the wafer W. When the supply of NH₃ gas is stopped and thesupply of HF gas is continued, the etching process proceeds by HF gas.When the supply of HF gas is stopped and the supply of NH₃ gas iscontinued, NH₃ gas may react with HF gas remaining near the wafer W andthis may result in over-etching. By stopping the supply of both gases atthe same time, a difference from a desired etching amount is reducedand, thus, the etching accuracy can be increased.

The effect of suppressing the microloading can be further enhanced bypre-mixing HF gas and NH₃ gas. In the dense pattern area, the volume ofthe grooves 63 is small. Therefore, in the case of separately supplyingHF gas and NH₃ gas, if one of the gases is firstly supplied, it isdifficult to supply the other gas. Accordingly, it is expected that thereaction of the SiO₂ layer with HF gas and NH₃ gas becomes slower andthe etching speed is decreased. By supplying HF gas and NH₃ gas in apre-mixed state, HF gas and NH₃ gas are supplied in a uniformly mixedstate to the grooves 63 even in the dense pattern area. As a result, thevariation in the etching speed of the SiO₂ layer 61 filled in thegrooves 63 is reduced regardless of the density of the pattern and thevariation in the etching amount of the grooves 63 is reduced.

Further, in the case of separately providing HF gas and NH₃ gas into theprocessing chamber 1, an area where HF gas and NH₃ gas is non-uniformlymixed exists locally on the surface of the wafer W. In such an area, theetching speed is decreased. Therefore, when the SiO₂ layer 61 is etched,the etching speed varies even at the same groove 63. As a consequence,irregularities on the surface of the SiO₂ layer 61 are increased and theroughness becomes poor. The poor roughness can be avoided by supplyingthe gaseous mixture of HF gas and NH₃ gas to the wafer W.

In the above-described embodiment, the gaseous mixture of HF gas and NH₃gas is intermittently supplied to the wafer W mounted on the processingchamber 1 of a vacuum atmosphere in the case of etching the SiO₂ layer61 where an etching area is partitioned by the walls 62 and stopping theetching before a base layer is etched. When the gaseous mixture of HFgas and NH₃ gas is supplied to the heated wafer W, the gases react withSiO₂, thereby generating a reaction by-product. The etching processproceeds by the sublimation of the reaction by-product. The adhesionamount of the reaction by-product (protective film) varies depending onthe density of the pattern. In the method of the present embodiment, thereaction by-product is sublimated (volatilized) by the heating of thesubstrate during the supply stop of the processing gas, so that theetching speed is constant regardless of the density of the pattern.Accordingly, the microloading is suppressed. Further, since HF gas andNH₃ gas are supplied in a pre-mixed state to the target substrate fromthe gas supply unit, the surface roughness is improved and themicroloading can be further suppressed as described above.

In the disclosure, as can be seen from the time chart of FIG. 11, thegaseous mixture of NH₃ gas and HF gas may be supplied in a pulsed mannerby supplying HF gas into the processing chamber 1 at the time t₁,supplying NH₃ gas at the time t₂, and stopping the supply of HF gas andNH₃ gas at the same time at the time t₃. The supply time Ta of thegaseous mixture is set to, e.g., about 2 sec. The supply stop time Tb ofthe gaseous mixture is set to about 5 sec.

In the above-described embodiment, when the supply of HF gas to thewafer W is stopped, HF gas flows toward the bypass line 56. In the caseof stopping the flow of the carrier gas to a hydrofluoric acid solutiontank as an HF gas supply source during the supply stop, the method ofFIG. 11 is effective in stabilizing volatilization of hydrofluoric acid.Therefore, it is preferable to select a gas to be supplied first betweenHF gas and NH₃ gas depending on semiconductor device manufacturingprocesses.

In the case of employing the sequence shown in FIG. 4 or 11, one of HFgas and NH₃ gas is supplied earlier than the other gas by ΔT, e.g.,about 0.5 sec to 15 sec. The time Ta at which the gaseous mixture ofboth gases is supplied preferably has a duration of, e.g., about 0.5 secto 5 sec. The supply stop time Tb of the gaseous mixture preferably hasa duration of, e.g., about 5 sec to 20 sec.

In this disclosure, HF gas may be intermittently supplied multiple timeswhile continuously supplying NH₃ gas into the processing chamber 1. Or,NH₃ gas may be intermittently supplied multiple times while continuouslysupplying HF gas.

Moreover, in this disclosure, HF gas and NH₃ gas may be supplied intothe processing chamber 1 at the same time in a pulsed manner. In thatcase, the gas supply and the supply stop are controlled by controllingopening/closing of the valves V3, V4, V7 and V8. When the gas supply isstopped, HF gas and NH₃ gas bypass the processing chamber 1 through thebypass lines 56 and 46, respectively, to be exhausted. In such aprocess, a period of time in which the wafer W is exposed to anatmosphere of the processing gas containing a mixture of HF gas and NH₃gas and a period of time in which the wafer W is not exposed to any oneof HF gas and NH₃ gas are alternately repeated multiple times.Accordingly, the concentration difference of each of HF gas and NH₃ gason the surface of the wafer W is reduced. As a result, the SiO₂ layer 61can be uniformly etched.

A diffusion member for diffusing gases radially in a horizontaldirection may be provided at downstream sides of the gas supply lines 33and 34. HF gas and NH₃ gas may be dispersed in the dispersion space 32and mixed with each other.

As an example of the silicon oxide layer on the target substrate wherethe etching area is partitioned by the pattern layers, the SiO₂ layer 61having on a top surface thereof Si mask patterns 66 as shown in FIG. 12may be used. In that case, the SiO₂ layer 61 is etched along the maskpatterns 66 and the etching is stopped before a base layer is etched.

The SiO₂ layer 61 can be etched by using a processing gas containingnitrogen, hydrogen and fluorine, such as ammonium fluoride (NH₄F) gas.In that case, the gas reacts with the SiO₂ layer 61, thereby generating(NH₄)₂SiF₆. Therefore, it is possible to suppress the microloading andimprove the surface roughness of the SiO₂ layer 61 by intermittentlysupplying ammonium fluoride (NH₄F) gas multiple times to the wafer Whaving the SiO₂ layer 61.

In other words, the disclosure is a method of intermittently exposing atarget substrate to a processing gas containing a gaseous mixture of NH₃gas and HF gas or a processing gas containing a compound of nitrogen,hydrogen and fluorine, such as NH₄F gas or NH₄FHF gas, multiple times.The processing gas may be a gaseous mixture of NH₃ gas, HF gas and NH₄Fgas (or NH₄FHF gas).

Test Example

In order to examine the effect of the disclosure, the uniformity of thesurface was evaluated by performing an etching process on the wafer W.As shown in FIG. 13, the wafer W has an area where the Si walls 62extending horizontally are formed in parallel in the SiO₂ layer 61. Suchan area includes an area 64 where the walls 62 are spaced from eachother by a gap of about 30 nm and an area 65 where the walls 62 arespaced from each other by a gap of about 90 nm. In the SiO₂ layer 61 asan etching target, the area 64 where the gap between the walls 62 issmall (30 nm) corresponds to the area 64 where the pattern forpartitioning the etching area is dense, and the area 65 where the gapbetween the walls 62 is large (90 nm) corresponds to the area 65 wherethe pattern for partitioning the etching area is sparse. In the testexample, the etching process was performed on the wafer W by using theapparatus shown in FIG. 1 by the sequence of FIG. 4. As described above,the periods of time Ta, Tb, and ΔT were 2 sec, 15 sec and 10 sec,respectively. The supply cycles were repeated 12 times. In a comparativeexample, an etching process was performed on the wafer W for evaluationby the same sequence as that in the test example by using a post-mixtype apparatus for separately supplying HF gas and NH₃ gas into theprocessing chamber 1 through the gas supply holes 31 of the gas supplyunit 3, instead of a pre-mix type apparatus shown in FIG. 1.

FIG. 14 is a cross sectional view of the wafer W after the etchingprocess of the test example. FIG. 15 is a cross sectional view of thewafer W after the etching process of the comparative example. Thesecross sectional views are obtained from results of monitoring SEM(scanning electron microscope) images. FIG. 16 shows a surface roughnessstate of the wafer W after the etching process of the test example. FIG.17 shows a surface roughness state of the wafer W after the etchingprocess of the comparative example. In the test example, the verticalposition of the surface of the SiO₂ layer 61 is substantially the samebetween the dense pattern area 64 and the sparse pattern area 65 asshown in FIG. 14. A difference between an average etched depth in thedense pattern area 64 and an average etched depth in the sparse patternarea 65 is about 1 nm or less, which is close to zero. In thecomparative example, a etched depth in the dense pattern area 64 issmaller than that in the sparse pattern area 65 as shown in FIG. 15 anda difference between an average etched depth in the dense pattern area64 and an average etched depth in the sparse pattern area 65 is greaterthan about 10 nm.

In the comparative example, bottom portions of the grooves 63 are etchedin a waveform as shown in FIG. 17. However, in the test example shown inFIG. 16, a etcheded amount is smaller and a flatness is higher thanthose in the comparative example. Therefore, the test example shows thatthe method of the disclosure can suppress the microloading and improvethe surface roughness of the SiO₂ layer 61.

While the disclosure has been shown and described with respect to theembodiments, it will be understood by those skilled in the art thatvarious changes and modifications may be made without departing from thescope of the disclosure as defined in the following claims.

What is claimed is:
 1. A method for etching a silicon oxide film on atarget substrate where an etching area is partitioned by a pattern layerand stopping the etching before a base layer of the silicon oxide filmis etched, the method comprising: heating the target substrate in avacuum atmosphere; intermittently supplying, as an etching gas, at leastone of a first processing gas containing a hydrogen fluoride gas and anammonia gas in a pre-mixed state and a second processing gas containinga compound of nitrogen, hydrogen and fluorine to the target substratefrom a gas supply unit in multiple cycles.
 2. The method of claim 1,wherein a time period of said supplying the etching gas to the targetsubstrate in each cycle is about 0.5 sec to 5 sec.
 3. The method ofclaim 1, wherein a time period of stopping said supplying the etchinggas to the target substrate in each cycle is about 5 sec to 20 sec. 4.The method of claim 2, wherein a time period of stopping said supplyingthe etching gas to the target substrate in each cycle is about 5 sec to20 sec.
 5. The method of claim 1, wherein the compound of nitrogen,hydrogen and fluorine is either NH₄F or NH₄FHF.
 6. The method of claim2, wherein the compound of nitrogen, hydrogen and fluorine is eitherNH₄F or NH₄FHF.
 7. The method of claim 3, wherein the compound ofnitrogen, hydrogen and fluorine is either NH₄F or NH₄FHF.
 8. The methodof claim 4, wherein the compound of nitrogen, hydrogen and fluorine iseither NH₄F or NH₄FHF.
 9. The method of claim 1, wherein in saidsupplying the first processing gas to the target substrate, one of thehydrogen fluoride gas and the ammonia gas is supplied to the targetsubstrate from the gas supply unit right before the first processing gasis supplied.
 10. The method of claim 2, wherein in said supplying thefirst processing gas to the target substrate, one of the hydrogenfluoride gas and the ammonia gas is supplied to the target substratefrom the gas supply unit right before the first processing gas issupplied.
 11. The method of claim 3, wherein in said supplying the firstprocessing gas to the target substrate, one of the hydrogen fluoride gasand the ammonia gas is supplied to the target substrate from the gassupply unit right before the first processing gas is supplied.
 12. Themethod of claim 4, wherein in said supplying the first processing gas tothe target substrate, one of the hydrogen fluoride gas and the ammoniagas is supplied to the target substrate from the gas supply unit rightbefore the first processing gas is supplied.
 13. A non-transitorystorage medium storing computer execuable instructions, wherein theinstructions, when executed by a processor, cause the processor toperform the method described in claim
 1. 14. A non-transitory storagemedium storing computer execuable instructions, wherein theinstructions, when executed by a processor, cause the processor toperform the method described in claim
 2. 15. A non-transitory storagemedium storing computer execuable instructions, wherein theinstructions, when executed by a processor, cause the processor toperform the method described in claim
 3. 16. A non-transitory storagemedium storing computer execuable instructions, wherein theinstructions, when executed by a processor, cause the processor toperform the method described in claim
 5. 17. A non-transitory storagemedium storing computer execuable instructions, wherein theinstructions, when executed by a processor, cause the processor toperform the method described in claim
 9. 18. A substrate processingapparatus comprising: a processing chamber having a mounting partconfigured to mount thereon the target substrate; a gas supply unit,having a plurality of gas supply holes facing the target substrate,configured to supply, as an etching gas, at least one of a processinggas containing a hydrogen fluoride gas and an ammonia gas in a pre-mixedstate and a processing gas containing a compound of nitrogen, hydrogenand fluorine to the target substrate mounted on the mounting part, avacuum exhaust unit configured to evacuate the processing chamber; and acontrol unit configured to output a control signal that controls the gassupply unit to intermittently supply the etching gas to the targetsubstrate from the gas supply unit in multiple cycles.
 19. The apparatusof claim 18, wherein the compound of nitrogen, hydrogen and fluorine iseither NH₄F or NH₄FHF.